【作者】 李英峰；

【导师】 于养信；

【作者基本信息】 清华大学 ， 化学工程与技术， 2011， 博士

【摘要】 受限流体的热力学和动力学性质与主体相流体存在着显著差异。本文应用密度泛函理论和分子模拟方法对固体表面、狭缝孔道和ZSM-5分子筛中流体的吸附、相平衡和传递性质进行了研究。基于改进的基本度量理论描述的硬球项，对吸引Helmholtz自由能泛函在零主体密度处进行二阶Taylor展开，对相关的Helmholtz自由能泛函采用权重密度近似结合MBWR状态方程表述，提出了一种新的权重密度泛函理论。精确预测了Ar在CO₂固体表面上的薄厚膜转变点、润湿温度和表面临界温度。应用GEMC方法研究了具有共沸点的L-J混合流体和CH₄/N₂/CO₂二元体系在狭缝孔道中的相平衡。壁面选择性增加可以使共沸体系的共沸点组成发生严重偏移甚至消失，可以改善体系的汽液相变选择性；孔宽对共沸点组成几乎没有影响但狭缝变窄使体系的相变选择性变差。非选择性狭缝中，壁面势的增强使各CH₄/N₂/CO₂二元体系p-x相图上移、汽化热降低、相变选择性变差且更容易超临界；狭缝变窄在强/弱吸引狭缝中带来不同影响：强吸引狭缝中体系的饱和蒸汽压和汽相密度减小而弱吸引狭缝中恰好相反。修正了吸附热统计方法并对超临界L-J流体在狭缝孔道中的吸附进行了GCMC模拟。结果发现：T*=1.5的L-J流体在吸引狭缝中还会出现汽液相变现象，且狭缝越窄、壁面势越强相变现象越明显。采用调整了电荷参数的Compass力场，模拟了NH₃在H-ZSM-5中的吸附和传递性质。吸附等温线和吸附热结果均与实验吻合良好。NH₃的吸附机理为：H⁺附近>孔道交叉位置>孔道其它位置。温度升高和浓度增加使NH₃扩散系数变大且均有利于H⁺附近的NH₃分子摆脱束缚。开发了适用于ZSM-5分子筛的力场并对NH₃和烷烃在H（Ag、Cu）-ZSM-5中的吸附进行了模拟。吸附等温线和吸附热均与实验吻合良好。在H-ZSM-5中，甲烷和乙烷在交叉位置外的孔道中密度略高，吸附热约为NH₃的1/6¹/4。烷烃和NH₃在H-ZSM-5中同时吸附时，烷烃对NH₃吸附的促进作用随碳链增长先加强后减弱直至变为阻碍作用；NH₃的吸附热随烷烃碳链加长和含量增加而变大；NH₃主要吸附在H⁺附近，烷烃主要吸附在H⁺附近外的孔道中但在之字型孔道中的吸附随碳链加长逐渐减少直至消失。NH₃在Ag（Cu）-ZSM-5中也主要吸附在离子周围，但一个离子可以存在多个吸附区域，即Ag-或Cu-ZSM-5中存在更多的活性位点。更多还原

【Abstract】 There are significant differences of the thermodynamic and kinetic propertiesbetween the confined and the bulk fluids. In this work, density functional theory andmolecular simulation are used to study the adsorption, phase equilibrium and transportproperties of fluid confined on planar solid, in slit-like pore and in ZSM-5.A new weighted density functional theory is proposed based on a modifiedfundamental measure theory for the hard-core repulsion, a second-order Taylorexpansion around zero-bulk-density for attraction, and a correlation term evaluated bythe weighted density approximation combined with Modified Benedict-Webb-Rubinequation of state. For the Ar/CO₂system，the thin-thick film transition，the wettingtemperature and the surface critical temperature are predicted accurately.The Gibbs Ensemble Monte Carlo（GEMC） simulation is used to investigate thevapor-liquid phase equilibrium of a binary Lennard-Jones（L-J） mixture with azeotropicpoints and the CH₄/N₂/CO₂binary mixtures. With the enhancement of the wallselectivity, the azeotropic point is shifted drastically and almost disappeared, theselectivity of the vapor-liquid phase equilibrium can be improved. The narrowing of thepore width almost has no influence on the location of the azeotropic point, but causesthe decreasing of the vapor-liquid phase selectivity. In unselectively slit-like pores, thestrengthening of wall-fluid interactions brings the up-shifting of thepressure-composition（p-x） phase diagram and the easier reaching of supercritical statefor each CH₄/N₂/CO₂binary mixture, and it also makes the vaporization enthalpy andthe vapor-liquid phase selectivity decrease. The narrowing of the pore width influenceson the phase behavior of confined mixture in different ways according to the wall-fluidinteractions: the p-x phase diagram shifts up and the density of vapor phase decreases instrong attractive slit-like pores, while that changes inversely in weak attractive slit-likepores. Grand Canonical ensemble Monte Carlo （GCMC） simulations are carried outfor supercritical L-J fluid, with a modified equation for the statistic of adsorptionenthalpy, and it is found that: at a reduced temperature T*1.5, a vapor-liquid phasetransition could be observed, which becomes more apparent with the narrowing of thepore width and the strengthening of the wall-fluid interaction.Using Compass force field with charge parameters modified by us, the adsorption and transport properties of NH₃in H-ZSM-5are simulated. The predicted adsorptionisotherm and adsorption enthalpy show good agreements with those from experiment.The mechanism of NH₃adsorption in H-ZSM-5is: locations around H⁺>the cross pointsof the pores>other positions of the pores. Both temperature rising and concentrationincreasing make the diffusion coefficient of NH₃increase and are benefit for thebreaking the strong interaction between H⁺and NH₃.A new force field for ZSM-5has been developed, and the adsorption properties ofNH₃and alkanes in H（Ag,Cu）-ZSM-5are simulated with it. Good agreements areachieved between the simulated adsorption isotherm and adsorption enthalpy andcorresponding experimental data. The adsorption concentration of methane and ethanein pores beyond the cross point is a little higher, and their adsorption enthalpy is about1/6¹/4of that of NH₃. When alkanes and NH₃are adsorbed in H-ZSM-5simultaneously, the promotion of alkanes on the adsorption of NH₃firstly increases andthen decreases as the length of the chains grows. But when the lenght of alkane exceedsheptane, the promotion effect changes into hindrance effect. The lengthening of thecarbon chain and the increasing of the alkane concentration both cause an increasing ofthe adsorption enthalpy of NH₃. The NH₃are mainly adsorbed around H⁺, while thealkanes are adsorbed in other positions of the pores and their adsorption in zigzag poresdecreases continuously with the lengthening of carbon chain until disappears. InAg（Cu）-ZSM-5, NH₃are also mainly adsorbed around metal ions. Several locationregions could be found around a metal ions, and it means that there are more active sitesin Ag-or Cu-ZSM-5when compared to that in H-ZSM-5.更多还原